Ever increasing energy use has caused dependence on fossil fuels (i.e. coal, oil, natural gas) and a substantial increase in greenhouse gas emissions: considered to be the root cause of global climate change (McIlveen-Wright et al., “A Technical and Economic Analysis of Three Large Scale Biomass Combustion Plants in the UK,” Applied Energy 112:396-404 (2013) and Agbor et al., “Integrated Techno-Economic and Environmental Assessments of Sixty Scenarios for Co-Firing Biomass with Coal and Natural Gas,” Applied Energy 169:433-449 (2016)). The goal to reduce greenhouse gas emissions levels has led to increased interest in biomass use (Agbor et al., “Integrated Techno-Economic and Environmental Assessments of Sixty Scenarios for Co-Firing Biomass with Coal and Natural Gas,” Applied Energy 169:433-449 (2016)).
Coal is one of the most important energy resources worldwide (Zhou et al., “Kinetic Study on CO2 Gasification of Brown Coal and Biomass Chars: Reaction Order,” Fuel 173:311-319 (2016) and Pei et al., “Investigation of the Feasibility of Underground Coal Gasification in North Dakota, United States,” Energy Conversion and Management 113:95-103 (206)). However, combustion of coal releases a number of air pollutants and coal mining leads to safety issues, contamination of groundwater, surface pollution, and greenhouse gas emissions. Coal combustion releases chiefly sulfur dioxide (SO2), nitrogen oxides (NOx), mercury, and particulate matter, as well as other pollutants. It is also a major source of greenhouse gas emissions into the atmosphere, predominantly as carbon dioxide (International Energy Agency, Reducing Greenhouse Gas Emissions: The Potential of Coal, in: Organisation for Economic Cooperation and Development, Paris, France (2005)). Solid waste disposal relies on significant land use. The efficiency of most pulverized coal power plants is less than 40% (Pei et al., “Investigation of the Feasibility of Underground Coal Gasification in North Dakota, United States,” Energy Conversion and Management 113:95-103 (2016)).
Pulverized coal power plants face two issues that must be addressed. The first is that low rank coal, accounting for half of the world coal reserves, should be blended with bituminous coal. This blending is deemed necessary, because low rank coal decreases the efficiency of power plants, as well as resulting in an increase in CO2 emissions, because of the high moisture content (25-75 wt %). Moisture leads to more than a 20% increase in the CO2 emission in comparison to bituminous coal (Traa, Y., “Is a Renaissance of Coal Imminent?-Challenges for Catalysis,” Chemical Communications 46:2175-2187 (2010); Li et al., “Pyrolysis and Combustion Characteristics of an Indonesian Low-Rank Coal Under O2/N2 and O2/CO2 Conditions,” Energy & Fuels 24:160-164 (2010); and Lee et al., “Two-in-One Fuel Combining Sugar Cane with Low Rank Coal and Its CO2 Reduction Effects in Pulverized-Coal Power Plants,” Environmental Science & Technology 47:1704-1710 (2013)). The second issue facing coal power plants is compliance with the renewable portfolio standards (RPS) and the cap-and-trade system implemented in many countries (Lee et al., “Two-in-One Fuel Combining Sugar Cane with Low Rank Coal and Its CO2 Reduction Effects in Pulverized-Coal Power Plants,” Environmental Science & Technology 47:1704-1710 (2013)).
Co-firing biomass with coal has the potential to reduce most of these emissions (Agbor et al., “Integrated Techno-Economic and Environmental Assessments of Sixty Scenarios For Co-Firing Biomass With Coal and Natural Gas,” Applied Energy 169:433-449 (2016)). However, co-firing has several operational disadvantages (Agbor et al., “A Review of Biomass Co-Firing in North America,” Renewable and Sustainable Energy Reviews 40:930-943 (2014)). Its lower bulk density and high moisture content, compared to coal, results in higher transportation costs. Differences in physical properties complicate direct blending of biomass with coal, making necessary separate storage, handling and feeding of biomass. The lower heating value and moisture content of biomass compared to coal results in boiler derating. Relatively high values of alkali exacerbate ash fouling while some forms of biomass contain high levels of chlorine, which increases corrosion of boiler tubes. Finally, the composition of ash in biomass is distinct from coal ash and may not meet ASTM specifications for concrete applications. Accordingly, co-firing can increase the cost of ash disposal.
The present invention is directed to overcoming the difficulties found in the art.